Furnace assembly for thermal analysis use

ABSTRACT

This invention relates to a heating furnace assembly which is adapted to be coupled to and become a part of a mass spectrometer adjacent to the ion source (usually) within the instrument. The furnace is a radiant heating device utilizing an elongated slotted tubular quartz tube having a helical wound resistance disposed around its wall as the heating means and is adapted to be controlled by means of temperature sensing means disposed within a separate thermal analysis cell which is adapted to be disposed within the heating tube in the furnace.

United States Patent I [191 Brady et al.

[ Nov. 20, 1973 FURNACE ASSEMBLY FOR THERMAL ANALYSIS USE [75] Inventors: Thomas P. Brady, Natick; Horst G.

Langer, Wayland, both of Mass.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

22 Filed: Mar. 13, 1972 21 Appl. No.2 233,942

3,560,627 2/1971 Langer 13/31 3,623,355- 11/1971 Langer c. 73/15 B 3,629,888 12/1971 Langer 13/31 3,629,889 12/1971 Langer et al.. 13/31 3,634,591 1/1972 Langer 13/31 Primary Examiner-Velodymyr Y. Mayewsky Attorney-William M. Yates et a1.

[57] ABSTRACT This invention relates to a heating furnace assembly which is adapted to be coupled to and become a part of a mass spectrometer adjacent to the ion source (usually) within the instrument. The furnace is a radiant heating device utilizing an elongated slotted tubular quartz tube having a helical wound resistance disposed around its wall as the heating means and is adapted to be controlled by means of temperature sensing means disposed within a separate thermal analysis cell which is adapted to be disposed within the heating tube in the furnace.

7 Claims, 3 Drawing Figures M055 spec/rome/er source FOR THERMAL ANALYSIS USE BACKGROUND OF THE INVENTION This invention relates to radiant heated furnaces adapted to receive a thermal analysis cell and particularly to furnace and cell insertion assemblies which are adapted for use under high vacuum conditions.

Accordingly, a principal object of this invention is to provide an improved thermal analysis cell receiving and heating assembly which is well adapted for use under high vacuum conditions and which is capable of more uniform control of the heating of a thermal analysis cell.

Another object of this invention is to provide an improved radiant heating furnace and thermal analysis cell receiving and heating assembly for use under high vacuum conditions in a mass spectrometer.

Mass spectrometers are sometimes equipped with devices which allow the heating of samples within the confinement of the mass spectrometer vacuum or within the ion source to allow the measurement of sample temperatures during the operation of the mass spectrometer, thus permitting carrying out the operation known as differential thermal analysis. During differential thermal analysis operations it is essential that the sample containing cell be heated so far as is practicable at a linear predetermined rate of heating, that the sample temperature is known and indicated at all times, and for differential thermal analysis operations the sample temperature is continuously compared with that of an inert material in the same cell as that holding the sample. In general, this requires that three thermocouples located in the thermal analysis cell should be precisely at the same temperature at all times unless a chemical reaction occurs in the sample. It is also of extreme importance that equal heat transfer is provided from the heat source furnace to the thermal analysis cell, that little and preferably no temperature gradient exists in the cell itself, that fast heat transfer is provided from the cell to the sample and that each thermocouple remains electrically insulated. In the past it has been FURNACE ASSEMBLY difficult to provide equal heat transfer from the furnace to the cell because of the geometry of the heating assembly of the furnace. In addition, to make a cell useful it must be possible to load a sample into the cell and introduce the cell with the sample into the furnace within a mass spectrometer without shutting down the operation of the mass spectrometer or its other associated evacuated systems.

In accordance with this invention, there is provided a furnace assembly which is generally cylindrical in overall configuration and is rigidly supported from a valved tubular thermal analysis cell input and sealing assembly.

' The heating part of the furnace comprises a hollow tubular vitreous member having an array of generally longitudinally extending elongated slots extending through its side walls and an electrical heater winding extending around the outer periphery of said side walls. The heating part is held in axial alignment with and surrounding the space to be occupied by the differential thermal analysis cell to be inserted into the assembly.

The heater winding is coupled to an external power source.

A tubular element having a heat reflective inner wall surface surrounds the heating part.

The assembly is inserted into a mass spectrometer adjacent to the ion source.

The invention, as well as additional objects and advantages thereof will best be understood when the following detailed description is read in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatical view showing apparatus in accordance with this invention coupled to a mass spectrometer;

FIG. 2 is a side elevational view, partly in section, of a furnace and cell probe insertion and sealing assembly in accordance with this invention, and

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2.

Referring to the drawing, and particularly to FIG. 1, there is shown a mass spectrometer 12 having a tubular member 14 extending perpendicularly therefrom. An additional tubular element 42 having a compression coupling 44 at its outer end and having a ball type vacuum sealing valve 40 adjacent to the member 14 is coupled to the outer end of the member 14. A cell-probe assembly 46 (See FIG. 2) is shown partly inserted into the entry and sealing assembly. A diffusion pump 52 is coupled by means of valve 54 and tube 56 to a fore pump 58 and by means of a tube 60 and valve 62 to the mass spectrometer 12. The tubular element 42 is coupled through tube 48 and valve 50 to the tube 56 between the valve 54 and the fore pump 58.

Referring now to FIG. 2 and FIG. 3, as well as to FIG. I, there is shown the mass spectrometer tube 12 having a tubular member 14 extending transversely therefrom adjacent to the ion source 22 of the mass spectrometer. The member 14 has an outwardly extending flange 16 (see FIG. 2) at its outer end. A metal plate 18 on which is supported the furnace and cell probe entry and sealing assembly 10 is sealed, as by the fillet 20, for example, to the flange 16. A threaded tube 68 extends transversely through the plate 18 generally in coaxial relationship with the member 14. A tubular element 42 containing a so-called vacuum ball valve 40 is coupled to the tube 68 be means of coupling 66. A seal-nut element 64 seals the tube 68 and element 42 (and coupling 66) against the plate 18 through which the tube 68 passes.

A coupling 30 having a flange element 28 welded thereto as at 32 is threadedly coupled to the end of the tube 68 which lies within the tubular member 14. A metal annular plate 92, usually copper or brass, and of substantially larger diameterthan the diameter of the coupling 30 is coupled to the top of the flange element 28 by means of screws 34 and insulatingspacer elements 36.

A tubular heat reflecting element 76 is supported between the plate 92 and an upper annular plate 74.

The annular plate 74, usually made of metal and at least approximately of the same outer dimension as the diameter of the annular plate 92, is disposed parallel to the plate 92 and is coupled thereto by the screws 34.

A heating assembly comprising a tubular member 38 is disposed between the annular plates 74,92 and held in position laterally by the annulus 84 whose inner opening fits closely but slidably around the tubular member 38.

The member 38 contains an array of elongated slots 82 (usually 4 or 6) disposed in a usually symmetrical array along its length. Usually the slots 82 are disposed parallel to the longitudinal axis of the member 38.

A heating coil 94 is disposed on the wall, usually the outer wall, of the member 38, its ends being held in position by loops 96 extending from the side wall of the member 38. The winding ends, 86a, 88a are coupled to insulated feed through lines 86, 88, respectively, and thence to a suitable electrical energization source (not shown).

In operation, with the mass spectrometer pumped down by the diffusion pump 52 and with valves 40 and 54 closed, the cell-probe 46 is inserted in the tubular element- 42 between the closed valve 40 and the opened compression fitting 44. The compression fitting is then tightened around the tube of the probe 46 and, after a sufficient reduction of pressure by means of the fore pump 58, the valve 50 is closed and ball valve 40 and valve 62 are opened. The cell-probe 46 is then slowly pushed through and past the compression fitting 44, past the valve 40 and into the furnace body in the space inside the hollow tubular member 38. The heating coil 94 is energized at a controlled rate from a controller energization source (not shown) in coordination with the readings from control thermocouples or other temperature sensing means in the sample cellprobe assembly 46 (their leads are brought out at the outer end of cell-probe 46), as is known to those skilled in the art of differential thermal analysis.

Because of the location of the furnace adjacent to the ion source 22, the material vaporized on heating of the sample material carried in the cell-probe 46 is emitted into the ion source area of the mass spectrometer, where the vaporized material is ionized and analysis of the sample by mass spectrometric means occurs simultaneously with the differential thermal analysis of the sample.

A cell-probe assembly which is adapted for use with this invention is disclosed and claimed in Horst G. Langer U.S. Pat. No. 3,623,355 entitled Differential Thermal Analysis Cell Assembly issued Nov. 30, 1971.

The tubular member 38 may be made of quartz or of a high temperature type glass of the Vycor type, for example. The material used to make the tube is an electrical insulator, has high heat stability and has the capability of allowing infared energy to pass through it.

The heater winding may be made of any suitable wire or strip material of suitable heating capacity.

The sleeve 76 usually has heat reflecting surface which directs heat towards the interior of the assembly.

. The sleeve, shown as made of metal, may advantageously be a glass sleeve with a mirror coating on its outer surface.

In the operation of the furnace assembly of this invention, a fast responding heat supply is generated by the unsupported portion of the resistance heater winding where it crosses a window or slot in the tubular member 38. Second, the tubular member 38 itself acts as a heat capacitor which will tend to keep the temperature increase constant, even when the voltage decreases across the heater winding.

The combination of fast responding free radiating heater wire and the quartz body, for example, of tubular member 38 for slow cooling response allows this furnace assembly to be used from low temperatures up to the melting point of the quartz or other material from which the member 38 is made.

The slots 82 are about 1.25 inches long and four to six in number in a tubular member 38 which is about 2 inches long, has an outer diameter of about 0.5 inch and an inner diameter somewhat greater than 0.375 inch in order to accommodate a cell-probe having an outer diameter of 0.375 inch.

The total area of the windows or slots 82 is determined by the temperature range of application of the furnace. For good response in low temperature regions of use, over one-half of the side wall area of the member 38 is utilized in the slots.

However, for efficient heating at high temperatures, e.g., above 400 C., high heat capacity and thus less window area is desirable.

What is claimed is:

l. A furnace and sample insertion assembly for use under vacuum conditions, comprising tubular means having an end part adapted to extend into an evacuable chamber, a hollow vitreous tubular member disposed in said chamber, said tubular member being supported in fixed longitudinal alignment with and adjacent to said end part, said tubular member having an array of generally longitudinally extending slots extending through the side walls thereof, and electrical heater winding means disposed along and around the outer peripheral surface of said tubular member said heater winding means extends at least along the length of said array of slots.

2. An assembly in accordance with claim 1, wherein said tubular means includes valving means in the part thereof which is not adapted to extend into said evacuable chamber.

3. An assembly in accordance with claim 1, wherein an inwardly directing heat reflecting element surrounds said tubular member and said electrical heater winding means.

4. An assembly in accordance with claim 1, wherein said array of slots covers at least half the peripheral surface of the side walls of said tubular member.

5. An assembly in accordance with claim 1, wherein said tubular member is mechanically supported from said end part of said tubular means.

6. An assembly in accordance with claim 1, wherein said tubular means is made of a vitreous material capable of withstanding temperatures of at least 400 Centigrade.

7. An assembly in accordance with claim 3, wherein said heat reflecting element is carried on the walls of a vitreous tube surrounding said tubular means. 

1. A 5furnace and sample insertion assembly for use under vacuum conditions, comprising tubular means having an end part adapted to extend into an evacuable chamber, a hollow vitreous tubular member disposed in said chamber, said tubular member being supported in fixed longitudinal alignment with and adjacent to said end part, said tubular member having an array of generally longitudinally extending slots extending through the side walls thereof, and electrical heater winding means disposed along and around the outer peripheral surface of said tubular member said heater winding means extends at least along the length of said array of slots.
 2. An assembly in accordance with claim 1, wherein said tubular means includes valving means in the part thereof which is not adapted to extend into said evacuable chamber.
 3. An assembly in accordance with claim 1, wherein an inwardly directing heat reflecting element surrounds said tubular member and said electrical heater winding means.
 4. An assembly in accordance with claim 1, wherein said array of slots covers at least half the peripheral surface of the side walls of said tubular member.
 5. An assembly in accordance with claim 1, wherein said tubular member is mechanically supported from said end part of said tubular means.
 6. An assembly in accordance with claim 1, wherein said tubular means is made of a vitreous material capable of withstanding temperatures of at least 400* Centigrade.
 7. An assembly in accordance with claim 3, wherein said heat reflecting element is carried on the walls of a vitreous tube surrounding said tubular means. 